The highly repeated DNA segments in the genome of the African green monkey (Cercopithecus aethiops) are being studied. These sequences can be classified in three groups on the basis of known structural features: tandem repetitions localized to centromeres, called satellites, short interspersed repeated sequences and long interspersed repeated sequences. A new monkey satellite (deca-satellite) with a ten base pair repeat unit has been found joined to another satellite. Deca-satellite is remarkable for its extensive polymorphism from one individual to another in the species. Multiple repeated sequence families have been shown to be dispersed within the monkey genome. Each family includes tens of thousands of copies of sequences several hundred base pairs long. Several of these may be moveable elements since they are flanked by short repeats of the region of the genome into which they are inserted.